The invention relates to a laser amplifier system comprising a solid body having a laser-active medium, an excitation source for producing an excited state of the laser-active medium, and an amplifier radiation field which passes multiply through the solid body and from which a laser beam can be extracted.
Such a laser amplifier system is known, for example, from EP 0 632 551.
In this laser amplification system, however, the amplifier radiation field is guided, even with multiple passes through the solid body, in such a way that the individual branches are reflected back on themselves.
The disadvantage of an amplifier radiation field formed in this way is that a high number of passes of the amplifier radiation field through the solid body can be achieved only with great difficulty.
It is therefore an object of the invention to improve a laser amplifier system of the generic type in such a way that the highest possible number of passes of the amplifier radiation field through the solid body can be achieved with the simplest possible optical means.
This object is achieved according to the invention, in the case of a laser amplifier system of the type described in the introduction, by the fact that radiation field guiding optics are provided, which make the amplifier radiation field entering the solid body in the form of a plurality of incident branches with locally different trajectories and leave the solid body in the form of at least one emerging branch with a trajectory locally different from the incident branches, and that the radiation field guiding optics have at least one deviating unit which forms, from at least one of the branches emerging from the solid body, a branch which enters the solid body with a trajectory locally separate from this emerging branch.
The advantage of the solution according to the invention is that it provides a straightforward way of achieving a large number of passes of the amplifier radiation field through the solid body, and at the same time, since the incident branches and the emerging branches respectively have locally different trajectories from one another, optimum utilization of the excited laser-active medium in the solid body takes place.
It is particularly favorable for the incident branches always to enter the same solid body.
It is even more favorable for the incident branches always to enter the same volume region of the solid body.
In order not to increase the size of the cross section of the incident branches formed in turn from emerging branches by the deviating units, provision is preferably made for the radiation field guiding optics to form the incident branch from the emerging branch after intermediate focusing.
The intermediate focusing may in this case take place independently of the deviating unit. In order to configure the beam guiding optics according to the invention as compactly as possible, provision is preferably made for the intermediate focusing to take place in the vicinity of the deviating unit.
A particularly expedient solution in this case provides for an intermediate focus lying between two deviating elements of the deviating unit to be produced by the intermediate focusing, which prevents the intermediate focus from lying directly in a deviating unit.
It is particularly favorable in this case, in order to arrange both deviating elements as far away as possible from the intermediate focus, for the intermediate focus to lie approximately centrally between the two deviating elements.
Since the intensity per unit area of the cross-sectional area of the radiation field increases close to the intermediate focus, provision is preferably made for the optical path between the two deviating elements lying on either side of the intermediate focus to be greater than a spacing between an input branch entering the deviating unit and an output branch emerging from the deviating unit.
It is particularly favorable in this case for the optical path between the two deviating elements lying on either side of the intermediate focus to correspond at least to two times the spacing of the input branch and the output branch.
A particularly favorable solution provides for the deviating unit to guide the amplifier radiation field in a loop which, in relation to an input branch and an output branch of the deviating unit, has an extent in an expansion direction which is greater than the spacing between the input branch and the output branch.
This expansion of the radiation field in the expansion direction provides the opportunity to maintain a spacing which is as large as possible between the deviating elements lying on either side of the intermediate focus.
Preferably, the extent of the loop in the expansion direction is at least two times the spacing between the input branch and the output branch.
In the scope of the exemplary embodiments described so far, it has been assumed that the radiation field guiding optics convert at least one emerging branch into an incident branch by employing a deviating unit.
The solution according to the invention may, however, be refined in a particularly straightforward way if the radiation field guiding optics convert a plurality of emerging branches into a plurality of incident branches by means of at least one deviating unit.
In the scope of the description of the individual exemplary embodiments so far, the way in which the respective incident and emerging branches of the amplifier radiation field are intended to be formed has not been discussed in detail.
In principle, it would be conceivable to embody them as divergent or convergent branches, albeit with the disadvantage that the cross section of the branches would become larger as the number of passes is increased.
In order to be able to keep the cross section of the incident and emerging branches the same size, and therefore to be able to use a volume region of the solid body with excited laser-active medium optimally for amplifying the radiation field, provision is preferably made for the radiation field guiding optics to form an amplifier radiation field in which the branches entering the solid body and the branches emerging from the solid body are collimated branches.
In order respectively to form a collimated incident branch in turn from a collimated emerging branch, provision is preferably made for the radiation field guiding optics to be designed as at least singly recollimating.
In this case, xe2x80x9crecollimatingxe2x80x9d means the conversion of a collimated radiation field via intermediate focusing into a collimated radiation field.
It is even better for the radiation field guiding optics to be designed as multiply recollimating, so that a plurality of collimated emerging branches can in turn be converted into a collimated incident branch.
During the formation of the incident branches and of the emerging branches, it is particularly favorable in terms of the formation of the amplifier radiation field for an intermediate-focused branch to be formed between the collimated emerging branch and the collimated incident branch by the radiation field guiding optics during each recollimation, that is to say when converting a collimated emerging branch into a collimated incident branch. This makes it possible to preserve the optical beam cross section in a particularly favorable way.
In terms of the interaction of the recollimation with the deviating unit, no detailed indications have been given so far. For instance, a particularly advantageous solution provides for the intermediate-focused branch required during the recollimation to pass respectively through a deviating unit according to the invention.
In principle, it would be conceivable to provide separate recollimating optics of the radiation field guiding optics for each recollimation.
Expediently, provision is made in this case for the intermediate-focused branch to travel along an optical path which corresponds to two times the focal length of the recollimation.
In terms of the design of the various recollimating optics, it would be conceivable to carry out different recollimations with different focal lengths. It is particularly favorable for all the recollimating optics to have the same focal length.
It is particularly favorable for a plurality of recollimating optics to be combined to form a radiation field shaping element.
A radiation field shaping element according to the invention, which causes at least one recollimation, may be designed as an element through which the amplifier radiation field passes, for example a lens system or, in the simplest case, a single lens.
As an alternative to this, it is also conceivable, however, to design the radiation field shaping element as a reflecting element.
In the simplest case, the radiation field shaping elements designed as a reflecting element is designed as a concave mirror.
Such a beam shaping element must, according to the invention, have a focusing element and a collimating element for each recollimation, so that conversion of a collimated emerging branch into the intermediate-focused branch and then conversion of the intermediate-focused branch in turn into a collimated incident branch is possible.
A solution in which a plurality of focusing elements and a plurality of collimating elements are combined to form a radiation field shaping element is particularly favorable.
It is particularly favorable in this case for this one radiation field shaping element to form collimating and focusing elements with different regions.
A particularly favorable embodiment of a radiation field shaping element provides for the radiation field shaping element to be designed rotationally symmetrically with respect to a mid-axis running through the solid body.
Such a rotationally symmetric design provides either a lens system which is designed and arranged rotationally symmetrically with respect to the mid-axis or a mirror system designed and acting rotationally symmetrically with respect to the mid-axis.
Such a mirror system is, in the simplest case, designed in such a way that the collimating and focusing elements are regions of a concave mirror designed rotationally symmetrically with respect to the mid-axis.
Such a concave mirror may, for example, be a parabolic mirror. It is also conceivable, however, to design this concave mirror as a toric mirror.
In terms of the number of deviating units, no detailed indications have been given in connection with the explanation of the individual exemplary embodiments so far.
For instance, an advantageous exemplary embodiment provides for the radiation field guiding optics to comprise at least two deviating units, each of these deviating units forming, from an input branch of the amplifier radiation field which is formed from one of the emerging branches, an output branch with a trajectory locally separate therefrom, from which the corresponding incident branch is formed.
In principle, it would be conceivable to provide a separate deviating unit for each incident branch to be formed from an emerging branch.
A solution designed in a particularly favorable way provides, however, for at least one of the deviating units to form, from at least two input branches formed from branches emerging from the solid body, at least two output branches from which the corresponding branches entering the solid body are formed, so that the number of deviating units can advantageously be reduced to two.
Furthermore, it is particularly favorable for the radiation field guiding optics to comprise two deviating units, and for an output branch of each of the deviating units to lead to the formation of a branch which enters the solid body, from which in turn, after is has passed through the solid body, an emerging branch is produced, from which an input branch of the respective other deviating unit is formed.
Such a solution permits, in a particularly favorable way, the two deviating units to be joined together, so that a particularly compact optical solution is obtained.
Further advantageous radiation field guiding optics according to the invention provide for them to comprise a first and a second deviating unit, and for the two deviating units, respectively by deviating the amplifier radiation field relative to a single deviating symmetry plane assigned to the respective deviating unit, to convert at least three input branches, formed from at least three different emerging branches of the amplifier radiation field, into at least three output branches which have trajectories correspondingly locally separate from the input branches and from which at least three incident branches are produced.
A further advantageous embodiment of the radiation field guiding optics according to the invention provides for the radiation field guiding optics to have at least one deviating unit, and for the deviating unit to form, from at least one input branch, an output branch which is offset in relation to a mid-axis of the radiation field guiding optics by an angular spacing such that at least one further input branch lies in the angle range between this input branch and the output branch formed therefrom.
A further particularly favorable solution provides for the radiation field guiding optics to have a first deviating unit, which deviates the amplifier radiation field relative to a first deviating symmetry plane, and to have a second deviating unit, which deviates the amplifier radiation field relative to a second deviating symmetry plane, and for the deviating symmetry planes to run at an angle with respect to one another, which preferably corresponds to 360xc2x0 divided by the sum of the incident and emerging branches arising during a pass of the amplifier radiation field through the radiation field guiding optics and the solid body.
The term xe2x80x9cpass of the amplifier radiation fieldxe2x80x9d is in this case intended to mean propagation of the amplifier radiation field through the radiation field guiding optics, during which the propagation direction is preserved.
In terms of the arrangement of the deviating symmetry plane relative to the mid-axis, no detailed indications have been given so far. A particularly favorable solution provides for the deviating symmetry plane to run parallel to the mid-axis.
It is particularly favorable for the deviating symmetry plane to run through the mid-axis.
In terms of the arrangement of the input branches and the output branches of the deviating units, no detailed indications have been given so far. For instance, it is particularly favorable for the input branches of the amplifier radiation field to have trajectories spatially separate from one another.
In this case, it is particularly favorable for the input branches of the amplifier radiation field to be arranged relative to one another at angular spacings around the mid-axis of the radiation field guiding optics.
It is furthermore advantageous for the output branches to have separate trajectories from one another.
It is likewise favorable in this case for the output branches to have separate trajectories from the input branches.
It is particularly expedient for the output branches to be arranged relative to one another and relative to the input branches at angular spacings around the mid-axis of the radiation field guiding optics.
It is particularly advantageous in this case for the input branches and output branches produced during a pass of the amplifier radiation field through the radiation field guiding optics to be arranged without overlap in the space around the mid-axis of the radiation field guiding optics.
It is even more advantageous for the input branches and output branches, as well as an incident branch of the amplifier radiation field, during a pass to be arranged without overlap in the space around the mid-axis of the radiation field guiding optics.
A particularly advantageous solution provides for the input branches and output branches to be respectively arranged in separate space segments around the mid-axis of the radiation field guiding optics, and to extend inside the space segments transversely with respect to their propagation direction.
Preferably, the space segments are arranged in such a way that they stretch over approximately the same angle range around the mid-axis.
Particularly advantageous space utilization is obtained when the space segments of the input branches and of the output branches, as well as the space segment of the incident branch, essentially enclose the mid-axis.
Further features and advantages of the solution according to the invention are the subject matter of the following description and the graphical representation of a few exemplary embodiments.